Found some switchback clips at Youtube, as I don't think I can visit some of them soon...
Ubasute (JR Shinonoi line : Nagano prefecture)
Close to my location but have never ridden on any trains there after I moved into Hakuba. The joint sound when the train going across the cross point is cool.
Tateno (JR Houhi honsen line : Kumamoto prefecture)
Trains go uphill by changing the direction to climb the Aso mountain. This train abouve goes strongly uphill, but when I rid on one in '76, it seemed too tough for the train to go up there.
Tsubojiri (JR Dosan honsen line : Tokushima prefecture)
I sometimes passed there but only with express trains, have never experienced the local trains there yet.